The present invention relates generally to optical lens supports and more particularly to ophthalmic lens supports.
It is standard practice to treat ophthalmic lenses after fabricating them to confer particular characteristics on them, for example abrasion resistance and/or antireflection properties. This is known in the art.
In the present context, and in the usual way, the expression xe2x80x9cophthalmic lensxe2x80x9d refers to a blank from which an eyeglass lens to be mounted in an eyeglass frame is then obtained by trimming.
The blank usually has a circular peripheral contour but this is not necessarily always the case.
The following description must therefore be considered to apply to any contour.
Be this as it may, applying a treatment to an ophthalmic lens usually entails depositing at least one layer of material onto its surface and it is obviously important for the deposit to be very uniform.
An antireflection deposit is usually applied in a vacuum.
This is the case, for example, in U.S. Pat. No. 2,532,971, in which ophthalmic lenses to be treated are each disposed in an individual support for holding them throughout their treatment.
The treatment in practice entails rotating the ophthalmic lenses at a relatively moderate speed, which is of the order of 50 rpm, about the rotation axis of a collective support to which the combination of the lens and its support is attached.
The individual support for each ophthalmic lens includes a base and three bearing studs carried by the base for holding an ophthalmic lens by its edge, one of which studs is fixed relative to the base, although its position relative thereto may be adjustable, and the other two of which are individually carried by elastically deformable arms carried by the base.
In practice the base takes the general form of a globally circular contour ring whose radial dimension, i.e. whose dimension in the direction of its thickness, and therefore in the plane of its edges, is very much less than its height, i.e. its dimension perpendicular to that plane.
In practice, the individual support in the general form of a ring, which itself has to be fixed into a ring, is never operative through the edge of its base.
More recent implementations are substantially the same, for example that described in U.S. Pat. No. 5,325,812, in which an individual ophthalmic lens support of the above kind is in practice reduced to a simple elastically deformable ring adapted to be fixed into a rigid support ring.
Another technique for depositing a layer of material, usually referred to as spin coating, has been developed for other types of substrate, namely silicon wafers used in the field of microelectronics, whereby the substrate is rotated and a small quantity of material is deposited on its surface.
The rotation speed of the substrate during the spreading of the material is relatively high, and higher than its speed of rotation during deposition of the material, and is in practice always greater than 1500 rpm, in order to spread the material correctly over the whole of the surface of the substrate.
Because of the high rotation speed used, it is obviously important for the individual supports of the substrates to be treated to be properly seated inside the corresponding apparatus.
For applying a treatment to an ophthalmic lens by spin coating, a support in the general form of a ring of the kind which is usually employed at present for holding an ophthalmic lens, as outlined above, would obviously not be suitable, because of its poor seating.
German patent application No. 38 38 012 describes a support for applying a treatment by spin coating to an ophthalmic lens, including three clamping members each of which consists of a support finger which receives the ophthalmic lens and a clamping finger which clamps the lens, with a flyweight system that varies the pressure applied to the lens according to the rotation speed.
The overall result is a particularly complex implementation.
A general object of the present invention is an optical lens support which, in contrast, provides a simple way of holding an optical lens correctly, even within apparatus using the spin coating deposition technique.
That optical lens support, which is of the kind including at least one first base and, carried thereby, for holding an optical lens by its edge, at least three bearing studs, is generally characterized in that, the base including, for its own seating, a plane bearing surface whose peripheral contour is globally circular, its radial dimension along any radius of that bearing surface is at least equal to its axial dimension perpendicular to the plane thereof.
There is obtained in this way a seating surface sufficient to enable use of the support in apparatus implementing the spin coating technique. The support can in particular be fixed by its single bearing surface on a turntable of the spin coating apparatus forming a pneumatic sucker, i.e. incorporating a plurality of suction orifices holding the base against said turntable by applying suction to its bearing surface.
It is even advantageously possible, thanks to the optical lens support according to the invention, to use existing apparatus, without any significant adaptation thereof, so obtaining the benefit in the field of optical lenses of a technology already proven in another field.
Generally speaking, it is advantageously possible, thanks to the optical lens support in accordance with the invention, to accommodate relatively high rotation speeds.
From this point of view, another object of the present invention is a method of using the support characterized in that it involves rotating the support and the optical lens it is carrying at a rotation speed greater than 500 rpm.
In a first embodiment, at least one of the three bearing studs is fixed relative to the base and at least one other is carried by an elastically deformable member itself carried by the base.
For at least some applications two of the bearing studs of the optical lens support in accordance with the invention are preferably fixed, only the third of the bearing studs being carried by an elastically deformable member.
It is therefore advantageously possible to control better the elastic force to which the optical lens is subjected even though, given the temperature to which it is subjected, which can be as high as 100xc2x0 C., and the fact that the elastic force is applied to its edge, which can be very thin, for some prescriptions at least, the optical lens can be made dangerously more fragile, so that it is desirable to protect it.
The bearing studs of the optical lens support in accordance with the invention are preferably operative along a circumference that is eccentric to the periphery of the base, i.e. relative to the periphery of the bearing surface thereof, the center of this circumference being nearer the fixed bearing stud or studs than the center of that periphery.
Good results have been obtained with the optical lens in its support off-centered in this way.
The base of the optical lens support according to the invention preferably has a central opening and the fixed bearing stud or studs are preferably on its border whereas the bearing stud or studs carried by an elastically deformable member are preferably inside the contour of the central opening.
It is therefore advantageously possible to treat both faces of the optical lens continuously, merely by turning over the combination of the lens and its support.
Furthermore, when two fixed bearing studs are used in this way, unwanted vibration in use is advantageously reduced, which has the benefit of improving the stability of the combination during the corresponding rotation.
Finally, the relatively small thickness of the base of the optical lens support according to the invention is also advantageous and beneficial in that it enables the support to be stored on edge in a storage rack having regularly spaced grooves into each of which a support can be inserted.
In a second embodiment the three bearing studs are fixed to the base and each has a radial bearing face and an axial bearing face, the axial bearing faces of the various studs offering a seat to the periphery of the lens in a specific plane parallel to the bearing surface of the base. The lens is held more rigidly and more reliably in this case, especially at high rotation speeds.
Because the base is in the form of a solid disk, the seating plane offered by the axial bearing faces of the studs is at a slight distance from the other face of the base.
Because the base takes the general form of a disk with a central opening delimited by an inside edge substantially the same shape and substantially the same size as the lens, each bearing stud is made in two parts, having a first part that projects from the other side of the base and features the radial bearing face of the stud concerned and a second part which projects radially from the inside edge of the base. The base then advantageously takes the general form of a disk with a central opening delimited by an inner edge substantially the same shape and substantially the same size as the lens and the bearing studs are each made in two parts, having a first part that projects from the other side of the base and features the radial bearing face of the stud concerned and a second part that projects radially from the inside edge of the base.
The second part of each stud is advantageously in one piece with the base. The beveled axial bearing faces therefore offer a pseudo-conical seat to the lens, which reduces its contact with these axial bearing faces to a line, or even a point, on its peripheral edge. This protects its lower face from any contact that could damage its surface treatment.
In accordance with an advantageous feature constituting an improvement to the invention, and still in the case where the three bearing studs are fixed, the support includes a second base, similar to the first one, provided with at least three bearing studs for holding the lens and having, for its own seating, a plane bearing surface whose peripheral contour is globally circular, its radial dimension along any radius of that bearing surface being at least equal to its axial dimension in a direction perpendicular to the plane thereof; the studs of the second base have axial bearing faces for seating the lens in a plane parallel to the bearing surface of the base for its own seating; the two bases are provided with means for assembling them in a superposed arrangement, with the bearing surface of each base facing away from the other base, so that the two seatings offered by the axial bearing faces of the studs of the two bases sandwich the periphery of the lens.
The lens is therefore sandwiched between the two bases, the axial bearing faces of the studs of each of which offer it a seating in a plane parallel to their bearing surface. The whole of the support, with its two bases and the lens placed between them, can therefore be turned over to treat the two faces of the lens successively. To treat a first face of the lens, the support is disposed so that the first base is under the second base, with its bearing surface resting on the turntable of the apparatus, the lens resting on the axial bearing faces of the studs of the first base. After treating this first face of the lens, the support assembly is turned over so that its second base is under the first base, with its bearing surface resting on the turntable of the apparatus. The lens then rests on the axial bearing face of the studs of the second base and its second face can be treated.
The two seating planes offered by the axial bearing faces of the studs of the two bases are then advantageously separated by a distance slightly greater than the thickness of the lens and the lens has some axial clearance between the two seating planes associated with the two bases. In this case, regardless of the position of the support, the upper face of the lens is entirely disengaged from the axial bearing faces of the studs of the base which is above it and its lower face, which is not treated, is only in contact with the axial bearing faces of the studs of the base that are resting on the turntable of the spin coating apparatus.
The means for assembling the two bases together advantageously make use of the bearing studs. The bearing studs therefore have a second function, contributing to assembling the two bases.
In an advantageous embodiment utilizing this feature, the bearing studs of the first base each include a lug parallel to the central axis, opposite the bearing surface of the base, and which carries the radial bearing face of the stud concerned, and the studs of the second base each include a post carrying the axial bearing face of the stud concerned and having an axial housing to receive the lug of a corresponding stud of the first base.
When axial clearance is required between the seating planes associated with the two bases, the separation of the two bases, and therefore of the two seating planes which are offered by the axial bearing faces of their studs, is preferably determined by abutment of the free end of the lugs of the studs of the first base against the back of the housings of the posts of the studs of the second base.
According to another advantageous feature, the axial bearing faces of the studs of the second base are beveled. As previously explained for the studs of the first base, the fact that the axial bearing faces of the studs of the second base are beveled offers the lens a pseudo-conical seating that reduces its contact with these axial bearing faces to a line, or even a point, on its peripheral edge. Its lower face, which may have just been treated before turning the support over, is therefore protected against any contact that could damage its surface treatment.
In a preferred embodiment, each of the two bases has the general form of a disk with a central opening in it delimited by an inside edge substantially the same shape and substantially the same size as the lens.